1. Field of the Invention
The present invention relates to a trap apparatus for use in an evacuating system for evacuating a vacuum chamber for a semiconductor fabrication apparatus or the like.
2. Description of the Related Art
A conventional evacuating system will be described below with reference to FIG. 16. In FIG. 16, a hermetically sealed chamber 201 comprises a process chamber for use in a semiconductor fabrication process such as an etching apparatus or a chemical vapor deposition (CVD) apparatus. The hermetically sealed chamber 201 is connected to a vacuum pump 203 through a discharge path 202. The vacuum pump 203 serves to increase the pressure of gases discharged from the process in the hermetically sealed chamber 201 to the atmospheric pressure. An oil-sealed rotary vacuum pump has heretofore been used as the vacuum pump 203. A dry pump is mainly used as the vacuum pump 203 at present.
If the degree of vacuum required by the hermetically sealed chamber 201 is higher than the ultimate vacuum of the vacuum pump 203, then an ultra-high vacuum pump such as a turbo-molecular pump is additionally disposed upstream of the vacuum pump 203. A discharged gas processing apparatus 204 is disposed downstream of the vacuum pump 203. In the discharged gas processing apparatus 204, gas components that cannot directly be discharged into the atmosphere because of their toxicity or explosive properties depending on the type of the process are treated by a process such as adsorption, decomposition, or absorption. Only harmless gases are discharged from the discharged gas processing apparatus 204 into the atmosphere. Necessary valves are provided at appropriate locations of the discharge path 202.
The conventional evacuating system has the following disadvantages.
In the conventional evacuating system, if reaction by-products contain a substance having a high sublimation temperature, then the gas of the substance is solidified while its pressure is being increased, and deposited in the vacuum pump. This tends to cause a failure of the vacuum pump.
For example, when BCl3 or Cl2 which is a typical process gas for aluminum etching is used, the process chamber discharges the remainder of the process gas of BCl3 or Cl2 and a reaction by-product of AlCl3 via the vacuum pump. AlCl3 is not deposited at the suction side of the vacuum pump because its partial pressure is low. However, while AlCl3 is being discharged under pressure, its partial pressure rises to cause AlCl3 to be deposited and attached to the inner wall of the vacuum pump, resulting in a failure of the vacuum pump. The same problem occurs with reaction by-products such as (NH4)2SiF6 and NH4Cl that are produced in a CVD apparatus for depositing films of SiN.
It has heretofore been attempted to heat the vacuum pump to pass the reaction by-products in gaseous state through the vacuum pump so that no solid substance is deposited in the vacuum pump. The attempt has been effective to prevent a solid substance from being deposited in the vacuum pump. However, it has been problematic in that a solid substance is deposited in the discharged gas processing apparatus disposed downstream of the vacuum pump, thereby clogging a filled layer in the discharged gas processing apparatus.
One solution is to install a trap apparatus upstream or downstream of the pump. The trap apparatus attaches products to a trap unit disposed in the trap apparatus, and hence previously removes portions (components) which will generate solid substances, for thereby protecting various devices provided at the discharge path. In general, however, the conventional trap apparatus has a poor trapping efficiency, and about 60% of the components of discharged gases flow through the trap apparatus without being attached to the trap unit and are attached to downstream pipes and devices. This is mainly because the discharged gases flow through a portion having a poor trapping efficiency between the inner wall of a container and the trap unit in the trap apparatus, and pass through the trap apparatus without being trapped.
The present invention has been made in view of the above drawbacks. It is therefore an object of the present invention to provide a trap apparatus which, in a film deposition process or the like, can increase the trapping efficiency while the necessary conductance on the hermetically sealed chamber side is being maintained, and increase the service life of the vacuum pump, protect a toxic substance removing device, and, in addition, can reduce the equipment cost and the running cost.
According to a first aspect of the present invention, there is provided a trap apparatus comprising: a discharge path for evacuating a hermetically sealed chamber through a vacuum pump; a hermetically sealed trap container extended across the discharge path and a regeneration path disposed adjacent to the discharge path; a trap unit disposed in the trap container for attaching a product in a discharged gas thereon and removing the product from the discharged gas, the trap unit being selectively located at the discharge path or the regeneration path; a valve element disposed on both sides of the trap unit and being movable integrally with the trap unit; and a sealing material mounted on an outer circumferential surface of the valve element so as to slide over an inner circumferential surface of the trap container when the trap unit is moved.
With the above arrangement, since the outer diameter of the trap unit can be designed to a near value to the inner diameter of the trap container, the contact efficiency of the discharged gas introduced into the trap container with the trap unit can be increased. Therefore, the trapping efficiency of products in the discharged gas can be increased while the conductance of the discharged gas and a predetermined exhaust capacity are being maintained without affecting the performance of the process in the hermetically sealed chamber or the vacuum pump. Further, since the trap unit is selectively located at the discharge path or the regeneration path, the regeneration of the trap to be carried out in an in-line manner, and hence the trap regeneration work can be simplified.
The hermetically sealed chamber may comprise a process chamber for a semiconductor fabrication device or the like. If necessary, a discharged gas processing apparatus for removing a toxic substance from a process gas is provided. The vacuum pump preferably comprises a dry pump which uses no lubricating oil in the discharge path in order to prevent contamination of the chamber caused by the back-diffusion of oil.
According to a second aspect of the present invention, there is provided a trap apparatus, wherein at least two trap units are disposed in the trap container to perform a trapping operation in the discharge path and a regenerating operation in the regeneration path simultaneously.
With the above arrangement, since it is not necessary to stop the device for the regeneration of the trap unit and to prepare a trap unit for replacement even in the case of operation for a long period of time, a continuous stable operation can be achieved in the hermetically sealed chamber. Further, it is easy to fully automate the system by using a suitable means for controlling timing of the switching.
When the trap unit is used as a temperature trap unit, a heat medium may be externally introduced into the trap unit. Heat of gasification of liquefied gas (for example, liquid nitrogen), cooling water, or a coolant is used as the heat medium. In another method, a thermoelectric element (a Peltier element), a pulse tube refrigerator, or the like is used to generate low temperature at the trap unit without the flow of any heat medium per se.
In the regeneration section as in the case of the trap unit, a heat medium may be used, or alternatively a heater, a thermoelectric element, spontaneous temperature rising or the like may be used. In the regeneration operation, a heat medium for regeneration (generally gas) may follow a regenerated gas or the like. Alternatively, the heat medium and the regenerated gas are recovered separately from each other. In the latter case, a regeneration medium path is separately provided.
An air cylinder may switch and drive the trap unit. In this case, an air-driven control unit comprising a solenoid valve and a speed controller may be used for control. Further, the air-driven control unit may be controlled by a sequencer or a control signal through a relay.
Methods for performing switching of the trap unit in a full automatic manner without manual operation include, for example, a method in which a sensor for detecting a pressure difference between a pressure before the trap unit and a pressure after the trap unit is provided and, when the detected value reaches a predetermined value, switching is carried out, and a more practical method in which a suitable switching time is preset. When one discharge path is provided for one regeneration path, since the trapping time is identical to the regeneration time, the capability for regeneration is preferably made higher than the capability for trapping so that the regeneration operation is completed earlier than the trapping operation.
According to a third aspect of the present invention, there is provided a trap apparatus, wherein the sealing material is mounted on an outer circumferential surface of the valve element so as to be expanded toward an inner circumferential surface of the trap container. Expanding the sealing material radially to bring the sealing material into close contact with the inner circumferential surface of the trap container can ensure sufficient hermetical sealing when the valve element is in a stop state (a sealed state).
When the valve element is moved, the sealing material is contracted radially to reduce the protrusion of the sealing material from the outer circumferential surface of the valve element. Thus, loads caused by sliding at the time of movement of the valve elements can be reduced, so that durability of the sealing materials can be increased.
In a preferred aspect of the present invention, the sealing material is brought into pressure contact with an inner circumferential surface of the trap container only when the sealing material is expanded radially. With the above arrangement, sufficient hermetical sealing can be achieved when the valve element is in a stop state (a sealed state). When the valve element is moved, loads on the sealing section can be minimized.
According to a fourth aspect of the present invention, there is provided a trap apparatus, wherein the valve element comprises means for radially expanding the sealing material by pressing the sealing material outwardly. With the above arrangement, the interior of the valve element can effectively be utilized, and hence a compact trap apparatus can be achieved.
In a preferred aspect of the present invention, the means for radially expanding the sealing material relatively moves a pair of members facing with each other or a pair of members having a tapered surface away from and nearer to each other, the tapered surface facing with each other and having a V shape extending outwardly in horizontal cross-section.
With the above arrangement, mechanically bringing a pair of members close to each other permits the sealing material to be expanded radially via vertical surfaces or tapered surfaces. Further, moving a pair of the members away from each other permits the sealing material to be contracted radially by the elastic force of the sealing material.
According to a fifth aspect of the present invention, there is provided a trap apparatus comprising: a discharge path for evacuating a hermetically sealed chamber through a vacuum pump; a hermetically sealed trap container having an inlet and an outlet and constituting a part of the discharge path; a trap unit disposed in the trap container for attaching a product in a discharged gas thereon and removing the product from the discharged gas; and a throttle section disposed at a suction port of the trap container for regulating a flow of a discharged gas in the suction port such that the discharged gas flows toward the inside of the trap unit.
With the above arrangement, the flow of the discharged gas is regulated at the throttle section so as to flow toward the inside of the trap unit, and introduced through the inlet into the trap container, and then spreads again and flows through the trap container. Therefore, a large part of the discharged gas can be surely brought into contact with the trap unit to increase the trapping efficiency without significant lowering in conductance. The opening area of the throttle section is preferably about 80% to about 90% of the area of the passage at the inlet in the trap container.
According to a sixth aspect of the present invention, there is provided a trap apparatus comprising: a discharge path for evacuating a hermetically sealed chamber through a vacuum pump; a hermetically sealed trap container having an inlet and an outlet and constituting a part of the discharge path; a trap unit disposed in the trap container for attaching a product in a discharged gas thereon and removing the product from the discharged gas; and a suppression section disposed at a discharge port of the trap container for suppressing a flow of a discharged gas in the discharge port.
With the above arrangement, the flow of the discharged gas introduced into the trap container can be suppressed, and hence does not flow smoothly from the outlet of the trap container. Therefore, the discharged gas stays within the trap container for a longer period of time, and hence the trapping efficiency can be increased by a longer period of contact of the discharged gas with the trap unit.
In a preferred aspect of the present invention, the trap unit may comprise a baffle plate having a curved trap surface. With the arrangement, a curved trap passage is formed to increase the probability that gas molecules in the discharged gas collide with the trap surface, thereby increasing the trapping efficiency.
In this case, the trap surface is preferably in the shape of an arc and an axis of the arc crosses the discharge path. With the above arrangement, a baffle plate having a curved trap surface is formed in a relatively simple way.
The above and other objects, features, and advantages of the present invention will be apparent from the following description when taken in conjunction with the accompanying drawings which illustrates preferred embodiments of the present invention by way of example.